This invention relates to asphaltic or bituminous roofing materials and methods, and more particularly to the manufacture of such roofing materials in which fly ash comprises the major part of the inert filler in the asphalt mix.
in the manufacture of roofing shingles or rolls, a heated asphaltic/filler blend is applied to a substrate web, such as a glass fiber mat or a felt. After the mat or web is impregnated with the asphaltic mix, a granular surface treatment may be applied to the hot asphaltic surface and rolled or pressed into place. The coated web composite is then cooled so that it may be cut and bundled as shingles, or formed into rolls.
Asphaltic or bituminous materials as used in the roofing industry are well known in the art, with examples being described in the U.S. patent of Mikols, U.S. Pat. No. 4,490,493 issued Dec. 25, 1984 and in the U.S. patent of Hansen, U.S. Pat. No. 4,405,680 issued Sep. 20, 1983. Prior to application to the substrate or base web, the asphalt is heated in an asphalt heater to a temperature of around 500.degree. F. The heated asphalt is then blended with an inert filler which has also been preheated to a temperature necessary so as not to chill the mix and to facilitate blending of the filler with the asphalt.
The choice of filler has traditionally been based on considerations of availability, compatibility, and cost. An inert filler material which has been preferred and used by many roofing plants is that of powdered limestone (calcium carbonate), usually at a rate of about 40% to 70% by weight of the mix. As noted in Mikols, other materials may be blended with the asphalt, such as block and antiblock polymers and thinners, as well known in the art.
The rate at which an asphaltic roofing material plant can effectively operate is limited by a number of factors. One such factor is that the rate of production must allow for sufficient cool-down time to permit correct cutting and bundling of the shingles. At some production facilities, high ambient temperatures impede satisfactory chilling of the asphaltic composite felt or web. In spite of the use of water cooled chill rolls, high temperatures require a slowing down of production during periods of high ambient temperature. Little attention seems to have been paid to the use of materials, such as the selection of a filler, which would enhance, rather than impede, the cooling of the hot composite.
Powdered limestone often has been a filler of choice as it is widely available at a relatively low cost, and is compatible with the asphalt mix. However, it is a poor conductor of heat when compared to fly ash. It is relatively slow to heat, and thereafter, in the mix, tends to insulate the asphalt and retard the cooling of the composite web.
Calcium carbonate (limestone) is an active base material, and it therefore tends to be acted upon by the weak acid in the precipitation (acid rain) and is believed to contribute to a shortened life of the roofing material. More importantly, the limestone filler has been documented as the cause of algae growth and discoloration in asphaltic shingled roofs. The principle, if not the only alga which attacks roofs is of the genus gloeacapsa, an organism which grows naturally in harsh environments on limestone cliffs, cement or limestone walls, and roofs formed with a limestone filler. The limestone filler material is thought to give the alga a competitive advantage over other microorganisms, since limestone is a sedimentary rock derived from marine organisms and is rich in nutrients. The carbonate released from the limestone is believed to provide a moderately alkaline environment that favors algal growth. Besides nourishment, the porosity of the limestone filler retains moisture and provides a growth surface for the alga.